Population Structure of Anisakis Simplex (Nematoda) in Harbor Porpoises Phocoena Phocoena Off Denmark

Abstract

The population structure and habitat selection of Anisakis simplex in 35 harbor porpoises off Denmark are described. The nematodes were collected from the stomach and duodenal ampulla and were categorized as third-stage larvae, fourth-stage larvae, subadults, and adults. The porpoises harbored 8,043 specimens of A. simplex. The proportion of adults and subadults increased with infrapopulation size. The number of development stages across infrapopulations covaried significantly (Kendall's test of concordance). Concordance was higher in hosts with the highest intensities than in those with low and medium intensities. All stages occurred mainly in the forestomach, but this trend was stronger for the adults. Adult and subadult sex ratios did not depart significantly from 1:1. Our data suggested that recruitment and duration of each stage were the main factors accounting for infrapopulation structure. The preference of A. simplex for the forestomach conformed with previous studies, but the narrower distribution of adults relative to other stages might indicate a strategy to enhance mating opportunities. Information on sex ratios of A. simplex is scarce and contradictory. We suggest that the discrepancies might partly reflect differences in categorization criteria and statistical methods.The occurrence of third-stage larvae (L3) of anisakid nematodes in the fillets of commercial fish entails well-known public health concerns and economic repercussions (Burt, 1994;Smith, 1999). Consequently, the population ecology of anisakid nematodes has received more attention than that of any other parasite of marine mammals. Most population studies of anisakids have focused on describing the population structure and dynamics of the sealworm, Pseudoterranova decipiens, and other species common in seals (see Bowen 1990; Desportes and McClelland 2001, and references therein for examples) and have produced valuable data on the life history and population ecology of these nematode species.As for the whaleworm, Anisakis simplex, most population studies have focused on its intermediate and paratenic hosts (Brattey and Bishop, 1992;Herreras et al., 2000;Podolska and Harbowy, 2003), whereas its population biology in the definitive hosts has been less studied. Most information on the definitive hosts concerns the harbor porpoise, Phocoena phocoena, a small odontocete common in the Northern Hemisphere (Smith, 1989;Brattey and Stenson, 1995;Herreras et al., 1997). The data on the population structure of A. simplex in this cetacean are based on small sample sizes (Young, 1972;Smith, 1989) or lack details of the infrapopulation structure (Lick, 1991;Brattey and Stenson, 1995). These 2 shortcomings are also common in studies of this nematode in other cetacean species (e.g., Wazura et al., 1986;Raga and Balbuena, 1993). Moreover, little is known about habitat selection by A. simplex in the definitive hosts. To our knowledge, there are only 2 studies providing such information (Brattey and Stenson, 1995;Aznar et al., 2003), and only the ...

Anisakid larvae in the liver of cod (Gadus morhua) L. from the southern Baltic Sea

“…The life cycles of these nematodes are similar and involve crustaceans and many species of fish that serve as intermediate or paratenic hosts, with marine mammals as the final hosts (McClelland et al , 1990). Important cetacean hosts for A. simplex that are also reported in the Baltic Sea are the harbour porpoise, Phocoena phocoena (Herreras et al , 2004), the white-beaked dolphin, Lagenorhynchus albirostris , and the common bottlenose dolphin Tursiops truncatus (Smith & Wootten, 1978). The grey seal, Halichoerus grypus , is considered to be the most important final host for C. osculatum (Fagerholm, 1990), and the common seal (harbour seal), Phoca vitulina , is the most important final host for P. decipiens (Aspholm et al , 1995).…”

First evidence of the presence ofAnisakis simplexinCrangon crangonandContracaecum osculatuminGammarussp. byin situexamination of the stomach contents of cod (Gadus morhua) from the southern Baltic Sea

“…The main final hosts for A. simplex in the Baltic Sea are cetaceans, namely the harbour porpoise, P. phocoena (Herreras et al ., 2004), the white-beaked dolphin, L. albirostris , and the common bottlenose dolphin, T. truncatus (Smith and Wootten, 1978). The density and distribution of harbour porpoise in the central Baltic Sea or Baltic Proper considerably declined during the last century (Koschinski, 2001).…”

“…The life cycles of A. simplex , C. osculatum and P. decipiens are similar and involve marine mammals as the final hosts (McClelland et al ., 1990; Klimpel and Palm, 2011). The following important cetacean hosts for A. simplex have also been reported in the Baltic: the harbour porpoise, Phocoena phocoena (Herreras et al ., 2004), the white-beaked dolphin, Lagenorhynchus albirostris , and the common bottlenose dolphin Tursiops truncatus (Smith and Wootten, 1978). According to Fagerholm (1990), the grey seal, Halichoerus grypus , is considered to be the most important final host for C. osculatum , while the common seal (harbour seal), Phoca vitulina , is the most important final host for P. decipiens (Aspholm et al ., 1995).…”

Ascaridoid nematode infection in haddock ( Melanogrammus aeglefinus ) and whiting ( Merlangius merlangus ) in Northeast Atlantic waters

“…in strandings of harbour porpoise (60%), common dolphin (71%) and white-beaked dolphin (5 out of 6 individuals) in England. Herreras et al (2004) found an average intensity of 230 Anisakis simplex in 35 harbour porpoise sampled in Denmark. The fact that the abundance of porpoise and minke whale is higher in the North Sea than on the west coast of Scotland (Hammond et al, 2013) may thus help explain the difference in infection rates in fish.…”